Nothing screams polished and put-together more than clothes that fit properly.

Decide what you're most comfortable it - a skirt suit, pants & blazer, dress with a cropped jacket or whatever - and then have those things altered to fit you properly - things they should check for are hemlines (always make sure you're getting fitted wearing the shoes that you'll wear with that outfit!), waist fitting right (not so loose it gapes in back but not so tight it cuts in either), not too much loose fabric around the hips and butt (which billows out and just looks sloppy), length of sleeves, button placement and waist/back darts on a jacket.

Get some good quality, well fitting basics and build your work outfits around it. For work, I always went with 3 pairs of pants (2 black, 1 grey), 2 midi length skirts (I'm very tall, so they're dead on knee length on me), a handful of dresses (black, grey, a muted floral, houndstooth and an ombre-ish one that went from grey to black) and then some rotating colours and accessories that I'd change out from time to time. Different shirts, belts, scarves and the like.

Personally I say go for colours and styles that you personally like and feel comfortable in, because you can always tell when someone isn't comfortable in what they're wearing. Don't worry about what you "should" wear as you colour (for clothes! Makeup and hair can make a huge difference if you actually get the right shades).

Hair and makeup I'm less helpful with - I just get my hairdresser to do what she thinks looks good in terms of colour (at the moment it's slightly darker than my natural shade on top with a very subtle balayage of brown through to rose gold in parts of it) and I rarely wear makeup so have NO clue about that.